Many elevators include an elevator rope slung over a sheave with one end of the rope supporting an elevator and the other end supporting a counterweight. The elevator moves when the sheave is turned by a motor.
Elevator systems follow a dictated velocity profile. At a floor, an elevator is held in place by a brake. After a demand has been made for elevator service (for example, by a passenger pressing a hall button) the brake lifts, a velocity profile is dictated to a motor drive and the elevator is commanded to move in the direction and at the velocity dictated. On geared systems, however, static friction, or "stiction," in the gear box holds the elevator in place even as it is being commanded to follow an accelerating velocity profile and motor torque is increasing. Eventually, enough torque builds up to break the force of stiction and the elevator jerks free suddenly. This jerk, as the elevator begins to move, is called start jerk. It can be felt by passengers within the elevator and usually causes discomfort. It is also generally greater in geared than gearless systems.
A better elevator would be created if one could be made with minimal start jerk.